These days media content such as music and video data is typically stored in electronic form and distributed electronically. This electronic storage and distribution reduces the costs involved in getting the media content to end-users. However, the move to electronic storage and distribution also facilitates unauthorised sharing and copying and unauthorised copying of music and video files costs the music and film industries significant amounts of money every year in terms of lost revenue.
Content generators have turned to digital rights management in an attempt to reduce the amount of unauthorised copying. Digital rights management (otherwise known as DRM) involves the use of technology to limit or control copying of data files. Typically Digital Rights Management systems control the ability of end users to copy files by encrypting or scrambling some or a portion of a media file. Access to the media file can then be controlled by limiting access to the means for unscrambling or decrypting that portion of the file. Decrypting normally requires an end user to obtain a cryptographic key. Such a key can either be provided directly to a valid end user or alternatively require an end user to access a central database to have their identity validated whenever a copy of a file is to be made.
Digital Rights Management systems suffer from a number of drawbacks. Validation of a user's identity can be cumbersome and intrusive. Although central control of access keys increases security, accessing a central database for validation data can be monitored and logging data about a user's use of specified media files can raise concerns about privacy.
Problems also exist with DRM systems where a user desires to transfer a media file from one location to another. This can require users to revalidate their right to use a particular file, which can be unnecessarily time consuming. If such rights are not revalidated a legitimate user can be prevented from using data that they have acquired and paid for.
Digital watermarks are features of media that are added during production or distribution. More specifically digital watermarks involve marking electronic files with a unique code, typically spread throughout the file so that a copy of file is rendered unique. The addition of data is normally such so as not to degrade the quality of the original. Rather, a number of items of data are slightly modified compared with an original in a manner, which does not change the apparent appearance of sound of an original. Thus for example the colours of individual pixels in image files can be slightly modified which result a pixel being rendered in a different colour where the differences between the original and the modified image are not detectable by the human visual system. Although not apparent in an output image, the water-mark data can, still however, be detected by a direct comparison with an original file to identify which items of data have been modified compared with an original. Digital watermarks can form part of a digital rights management system.
Due to the limitations of conventional Digital Rights Management systems, alternative approaches are required or desirable.